This invention relates to clean air systems, and in particular, to a system for creating clean air zones in a clean room using the HEPA filters already in position in the clean room.
Laminar flow hoods are typically used to create a clean zone in a work room to contain chemical, biological agents, drugs and other hazardous substances and prevent their release into the atmosphere. A typical laminar flow hood has three sides, a bottom, and a top with a fan-forced source of forced air directed from one of the sides (usually the top or back side) through micro-filters or HEPA (High Efficiency Particle Air) filters. These cabinets are sold on the open market as free-standing units having cabinet walls on three sides with an open-front on one side and a top and a bottom comprised of almost any solid construction material, such as wood, steel, aluminum, hard plastics, or other materials. A HEPA filter is placed behind a porous wall on the top or a side of the cabinet, and an electric fan is positioned behind the HEPA filter to force air through the filter and into the cabinet.
There are generally two types of laminar flow hoods. The first, shown in FIG. 8, is a horizontal laminar flow hood. In a horizontal laminar flow hood, air is usually forced from a side or rear of the cabinet through a porous wall so that the air flows through the filter in a horizontal direction. The filtered air is free of particles over 0.5.mu.. The second type, shown in FIG. 9, is a vertical flow hood. In a vertical flow hood, the air is forced from the top of the cabinet through the HEPA filter, and then exhausted through the front opening of the cabinet to the room in which the cabinet is located. Vertical flow hoods or biological safety cabinets (BSC's) are particularly suited to protect workers or users of the cabinet from substances which may be manipulated inside the cabinet, such as toxic or irritant chemicals, dust, drugs, or biologicals, as well as to protecting the environment. The vertical flow hood in FIG. 9 is a BSC, and as seen, the air flow comes down through the top of the cabinet and passes through the bottom of the cabinet, so that none of the contaminants within the cabinet will escape into the room in which the cabinet is positioned.
In recent years, these cabinets have been used in industry for the clean manufacture of items such as computer chips, parenterally-administered medications, tissue cultures, cell cultures, microbiological testing, chemical mixing and the like. The principal differences in the use of the two types of cabinets or laminar flow hoods is that, although it provides a super-clean air work environment, the horizontal flow hood does not protect the worker from the materials used or manipulated inside the cabinet; but, the vertical flow hood does provide some protection as well as provide a super-clean air work environment.
The most common use of such cabinets has become medical related uses. These hoods are used for mixing medications and fluids for intravenous delivery into the patient for prevention, diagnosis, treatment, mitigation or cure of diseases. These cabinets are widely used, therefore, in hospitals, clinics, pharmacies, home infusion centers, and the like for the purpose of compounding, mixing, labeling or otherwise preparing medications.
Additionally, the vertical flow hoods are typically required to be used in a clean room--a room specially designed to have very low counts of particles in the air. For example, a clean room may have only 10,000 or 1000, or 100 particles per cubic foot of air in the room. Clean rooms are also required by some governmental agencies, such as state boards of pharmacy, or the US. Food and Drug Agency, and by professional standard making organizations, such as the American Society of Health Systems Pharmacists, the ISO 9000 standards for Parentaeral pharmaceutical manufacturing, and so on. In the instance of state boards of pharmacy, there is often a legal regulatory requirement that such environments include a clean room in which the air-born particles over 0.5.mu. in size number less than 10,000 per cubic foot of air, and that the clean zone (the table-top work area in which the actual mixing, compounding, manipulation, etc.) is performed have less than 100 particles per cubic foot of air. These standards are generally referred to as Class 10,000 or Class 100 work environments, or Class 10,000 or Class 100 laminar flow hoods.
Heretofore, to provide a Class 100 clean zone in a clean room required the use of a laminar flow hood, such as shown in FIGS. 6 and 7. The laminar flow hoods, whether vertical or horizontal flow hoods, are very expensive to purchase and to set up. Once they are set up in a clean room, the laminar flow hood is essentially fixed in place. The hood cannot easily be moved should the clean room need to be reconfigured or if the hood must be moved to a different room.